The present invention relates to a valving mechanism for microfluidic devices and more particularly to a valving mechanism which is controlled or actuated by electroosmotic flow (EOF). The invention also relates to a device for delivering fluid reagents which is actuated by EOF.
One example of a valving mechanism for a microfluidic device is described in U.S. Pat. Nos. 4,304,257; 4,858,883 and 5,660,370 to Webster and others. That mechanism employs a flexible sheet or diaphragm which is moved toward or away from a flat non-flexing sheet member having a pair of fluid ports such that flow between the ports is easily regulated. In one embodiment disclosed in U.S. Pat. No. 5,660,370, the diaphragm is attached to the plunger head of a solenoid which is operated to move the diaphragm between blocking and non-blocking positions to activate the valve. In another embodiment disclosed in U.S. Pat. No. 4,858,883, the diaphragm overlies a concavity which is connected to a source of vacuum or pressure which controls the valve. Other microvalve constructions useful in microfluidic devises are described in International Application WO 97/21090. These constructions include a piezoelectric element in which an applied voltage is used to deform the element and block fluid flow; a diaphragm which includes a bimetallic element which is resistively heated to proportionately deflect the diaphragm; an electrostatically activated plunger which is moved into a gap in the microfluidic; and a single-use valve fashioned from polymers which are stretched under defined condition such that when the polymer is subsequently heated, the polymer chains relax and thereby actuate the valve.
Electroosmotic flow (EOF) has been proposed as a means for moving solutions within a microfluidic device. In accordance with the present invention, two valve constructions are proposed for valves which utilize EOF to control the flow of a fluid between two ports. In one embodiment EOF is used to generate sufficient pressure to actuate a diaphragm valve. In another embodiment, EOF is used to control flow through a membrane which functions as a gate which is opened and closed electrokinetically. Another manifestation of the invention is a fluid delivery device in which EOF is used to move a diaphragm into a reservoir containing a reagent and in turn to meter the reagent into a microfluidic device.